1. Field of the Invention
This invention relates to a dielectric ceramic for microwaves having a high Q value suitable as a resonator and a circuit substrate material in a micro wave area.
2. Description of the Related Art
In recent years, dielectric ceramic have been widely used in a microwave area with the commercialization of automobile telephones, cordless telephones, personal wireless machines, and satellite broadcast receivers. Such dielectric ceramics for microwaves are used mainly in resonators. The characteristics required by the dielectric ceramics are the following three. (1) In the dielectric, the wavelength is shortened to 1/.epsilon.r .sup.1/2 (.epsilon.r: specific permittivity). Accordingly, the specific permittivitv is large for the requirement of a smaller size. (2) At high frequencies, the dielectric loss is small, and therefore, the Q value is high. (3) Resonant frequencies vary little to the temperature; namely, the temperature dependence of the specific permittivitv is small and stable.
Heretofore, the known dielectric ceramics of this type include complex oxide dielectric materials such as BaO-TiO.sub.2 type materials, BaO-REO-TiO.sub.2 (wherein REO is a rare earth element oxide) type materials, MgTiO.sub.3 -CaTiO.sub.3 type materials and complex perovskite type materials.
Furthermore, among the aforementioned three requirements to the dielectric ceramics for microwaves, they are recently required to have a high Q value with higher frequencies of the used frequencies and larger electrification.
As shown in K. Wakino et al., J. Am. Ceram. Soc., 67,278 (1984), impurities in the crystal grains or impurity phases are eliminated. Attempts have been made to arrange cations regularly in complex peroviskite type materials as shown in S. Kawashima et al., J. Am. Ceram. Soc., 66,421 (1983).